In vertical formwork, what a lot of people picture is the form of a wall or a column. But on a high-rise, you need to build one floor, then the next. All the equipment you have to build one floor has to be physically moved up to the next which is often done by a crane. And it’s a lot of material to move.
Hydraulic or self-climbing forms have evolved out of this situation because there isn’t enough time in the day—or in the construction cycle—for the tower crane to move all the forms for every project advancing formwork from one level to the next without the use of a tower crane. Here are seven facts about self-climbing systems that you might not know about.
They’re Fast, but Not in the Way You’re Thinking
You can absolutely construct a building without a self-climbing system, people have been doing this for thousands of years— it’ll just take longer. Let’s say you have 20 or more platforms to move independently and each platform can take 20 to 30 minutes to cycle just for moving the core formwork. If you have seven days to do so, that might be just fine. But if you have less days scheduled for your construction cycle, say four or even two, that’s the scenario that drives a self-climbing system forward.
Here you can take what could be an entire day operation and condense it into just a few hours without any (or at least minimal) interaction of a crane. This frees that crane up to allow it to work on the other parts of the project.
PERI
They’re Actually Fast, You Just Can’t Really Tell
Hydraulic-powered self-climbing systems can climb at just about 8 in. a minute. This means, that in 20 minutes, the machinery is actually traveling over 13 ft.
While a shorter pour may be quicker and taller pours might take a bit longer, the speed is set just to be right in a special zone to not shift anything while climbing up. What takes up most of the time is the removing of the bolts, preparing the system, and resetting, but these shouldn’t be rushed. Considering the weight that’s being carried along contractors have called it a “comfortable speed.” A speed that you would barely tell that it’s moving should you be on it while active.
These moves are known as “jumps.” From floor 2 to 3 is one jump.
These machines are expensive and projects typically require a certain duration—or a certain number of jumps—to warrant their use. That’s the tipping point of where time savings vs the cost of renting such a system swings in our favor. Other than high-rise buildings think bridge pylons for cable-stayed bridges, bridge piers. Basically, any project that is planned to be tall enough or where crane access might be difficult.
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A 160 Ton Push-Up
We already spoke to the speed of the hydraulics, but here this is all about strength.
For example, PERI’s ACS-400 system features four hydraulic cylinders, each one with a 40-ton capacity. And it all moves up with just a push of a one button. ACS stands for Automatic Climbing System, by the way.
Each hydraulic cylinder is synchronized with each other with an intelligent pump providing power to each cylinder simultaneously. This ensures that it climbs level. Remember what we said earlier, instead of working with 20 different crane picks, these allow you to lift the entire core box as one unit. It’s important here to note what can be lifted—because it’s not just the formwork. There’s all the tools, the generators, the hydraulic equipment, the pumps, a working corridor, stair tower access platforms. Some self-climbing systems even include the capability of installing a concrete placing boom.
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They’re Self-Sufficient
Some systems on the market need to have, what you would just call a starter wall. This is the first piece of concrete that the system has to mount to. There are others that don’t and are capable of using the integrated forming in the system to create that starter, then it just starts climbing.
Just like planning, it’s all in the set-up sequence to get things right from the ground floor. From there on, after that first pour and after a crane helps install the system, it’s on its own.
According to my sources at PERI, they’ve gotten installation down to about four days for a typical core. But that’s with the right crew size, crane availability, and site logistics. There are a lot of connections, pre-assembly, and engineering they integrate in order to speed up install time.
With a placing boom installed, contractors will be then able to start doing slab on grades and other columns. The faster you can get the core independent from the crane and self-sufficient the better. There’s when you can get everything else going on the project. Typically a self-climbing system will be able to climb up to set up for the next floor’s core the day after pulling the forms. To illustrate, if you pour level five today, you can then strike the forms tomorrow morning, then climb up to what will be level six the next day. The anchors are designed to work with the green concrete.
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They Can Be Manned By a Smaller Crew
If you look at projects here in the U.S., there’s typically one tower crane. It’s different over in Europe where you have a lot more tower cranes for a project – but it’s a different kind of perspective on building.
The tower crane’s cost itself is significant and there are operator costs. Where you may have a team of eight workers tied up for a whole day jumping a traditional system, you might have three or four tied up for two to three hours jumping a self-climber.
Consider this in areas with higher labor costs than others. According to sources, this could be indicative to why you might see more self-climbing systems in these areas than others.
Another factor is safety. Because everything in that box is being moved together, all those stay together, and move as one.
PERI
Work with a Buffer
With a lot of construction, you’re pouring the slabs and then the vertical walls. Then, those wall forms are jumped to the next level of slabs at the same time. Sometimes, it’s common to take the walls up ahead of the slabs. The core and walls can run ahead of the slabs by three or four stories. You don’t need to do one and wait for the slab beneath. If the self-climbing system is ready to go create the next level core, it can.
There are a couple of driving factors for why a high rise would be built this way. One, it reduces the risk of operation if there’s a problem. For example, if there’s a problem with the core and you miss delivery of rebar or the rebar for the core is late, you’ve minimized the impact.
Secondly, this method separates the work so two totally different crews can keep working out of each other’s way. If everyone’s working the same slab all those trades can be on top of each other and potentially slowing down the schedule. The self-climbing system working ahead lets everyone do their own thing at any given time. For example, while carpenters are working exclusively on the core, slab operations can focus on their job. All the trades aren’t conflicting with each other with a buffer between the two.
The next time you’re looking up at a high rise, think about that contractor. Think about the one person managing all the schedules so that subcontractor A can get to work all while subcontractor B is getting their job done out of everyone’s else way. Think about that hydraulic robot, climbing up the core of the building that it’s building as it crawls along.
